Regarding charging when at a low SOC at high ambient temperature. Definitely yes. When the car is charging it will also condition/ cool the battery pack. Under any extreme temperature, the car should be plugged in, even if not charging to take advantage of battery conditioning.
@klaus
"I don't think they're on public roads with the mules yet?"
These ARE on public roads. Just saw one in the atrium of the GM Powertrain HQ on Monday (July 22nd 2015). Tires showed heavy wear, mud on the sides, and a MI license plate on the back. Car was in full camo and had covers on...